Lightning near launch pad scrubs liftoff of SpaceX supply ship

Stormy weather near NASA’s Kennedy Space Center kept SpaceX’s Falcon 9 rocket on the ground Thursday, delaying liftoff of a commercial supply ship with equipment and experiments for the International Space Station until Saturday.

SpaceX’s launch director called off the launch attempt around 25 minutes before the scheduled blastoff from launch pad 39A at 5:55 p.m. EDT (2155 GMT), moments after a lightning strike at nearby Merritt Island violated the Falcon 9’s launch weather rules. The constraints state that at least a half-hour must pass since a lightning strike within 10 miles of the launch pad before liftoff.

Light rain and thunder were observed over the spaceport throughout Thursday afternoon, but SpaceX pressed ahead with the countdown and began fueling the 213-foot-tall (65-meter) rocket with cryogenic liquid oxygen and RP-1 kerosene.

There will not be a launch try Friday because time-critical science payloads stowed inside the Dragon supply ship at the top of the rocket must be changed out. The next launch attempt will be Saturday at 5:07 p.m. EDT (2107 GMT).

The unpiloted spaceship will carry 5,970 pounds (2,708 kilograms) of cargo to the space station, including a novel astrophysics experiment to study super-dense neutron stars and 40 mice for tests of a therapeutic drug designed to promote bone growth.

The launch delay means the Dragon spacecraft will miss its scheduled Sunday arrival at the orbiting research complex, opening up an opportunity for the station crew to release another supply ship that has been attached to the outpost since late April.

The countdown clock at the Kennedy Space Center press site on hold as lightning scrubs the Falcon 9 launch. Photo: Steven Young/Spaceflight Now.

Orbital ATK’s Cygnus cargo freighter, loaded with trash and other unneeded items, will now depart the space station Sunday, more than a month earlier than planned. If the SpaceX supply ship arrived Sunday, as originally intended, the astronauts aboard the space station would have been too busy unpacking cargo and conducting experiments delivered by the Dragon to manually release the Cygnus, which is bolted to a different berthing port than the one Dragon will use.

The Cygnus spacecraft is already packed with gear and garbage, and is “essentially” ready for departure, a NASA spokesperson said. It will deploy CubeSats and perform a fire experiment before re-entering Earth’s atmosphere and burning up June 11.

Meanwhile, cosmonaut Oleg Novitskiy and astronaut Thomas Pesquet will undock from the space station Friday inside a Soyuz ferry ship and land in Kazakhstan several hours later, reducing the station crew size to three until fresh residents arrive in late July.

If it launches Saturday, the Dragon will rendezvous with the space station Monday, and the station crew will grapple it with the research lab’s robotic arm around 10 a.m. EDT (1400 GMT) for berthing to the Harmony module.

SpaceX is flying a refurbished Dragon spacecraft for the first time. The pressurized portion of the supply ship set for launch Saturday first flew to the space station on a 34-day mission in September and October of 2014.

The Falcon 9 rocket slated to launch the capsule is new.

The U.S. Air Force’s weather forecast for Saturday calls for a 70 percent chance of acceptable conditions — the same outlook for Thursday’s launch opportunity — with anvil clouds and cumulus clouds from nearby storms the prime concerns. Skies should be overcast, and winds are predicted to be from the east-southeast at 12 to 17 mph.